The growth of the oral and pharyngeal structures and their respective cavities - that define the vocal tract (VT) - follow a prenatal to postnatal developmental continuum. Current theory asserts that postnatal growth of the VT is guided by the functions it serves, especially for the period from birth to early childhood where growth entails changes in size, shape, and relative proportions. Acoustic theory posits an evolving relationship between the VT anatomy and the properties of speech sounds during development. The available anatomic information is inadequate to explain the full nature of this relationship. Since 2000, our VT Development Lab has made steady progress towards its mission to quantitatively characterize sex-specific anatomic changes of the supralaryngeal speech system during development using a two-pronged anatomic-acoustic approach that entails: A. Anatomy: 1) Establishing a unique imaging database, consisting of 1679 imaging studies across the lifespan, that is representative of typically developing individuals of both sexes. 2) Compiling a large set of two dimensional landmark based measurements that capture the concurrent growth of the VT structures throughout the lifespan; and advancing novel analysis methods using select 3D models to quantify multidimensional growth (Chung et al. 2013, submitted) 3) Characterizing systematically the individual and relational growth of VT structures (Vorperian et al. 1999, 2005, 2007, 2009 & 2011). B. Acoustic: 1) Synthesizing findings on the development of vowel acoustic space i.e. the acoustic output of the developing VT (Vorperian & Kent, 2007). 2) Synthesizing findings on speech impairment in DS to help guide future research efforts (Kent & Vorperian, 2013). 3) Beginning to establish an acoustics database consisting of recordings from 250 participants including 90 individuals with Down Syndrome (DS) between the ages four to adulthood; and 4) Compiling developmental acoustics data including measures of the first four formants and their bandwidths. This proposed project combines imaging, acoustics, and VT modeling to study the development of the supra-laryngeal speech apparatus throughout the lifespan within the theoretical construct on function driven craniofacial growth. Research goals are to: 1) Capitalize on the imaging database to quantify the 3D growth of individual, relative and relational growth of VT structures while taking into account the structures' tissue type (bony, soft, cartilage and cavity), embryologic origin, plane of growth, and/or functional use. Also, extend our acoustics database while addressing fundamental issues in acoustic analysis. 2) Assess hypotheses that are acoustically driven and/or guided by structure/function interplay using typically and atypically developing individuals; and 3) Use age and sex-specific VT models to test hypotheses on anatomic-acoustic relationships. Project findings will provide a coherent and much needed picture on the development of VT structures throughout the lifespan. Such information is foundational for both theoretical constructs and clinical application in multiple disciplines that deal with craniofacial structures and functions.